I love this place. I can always find a useful answer to any
question. :-)
I'm thinking 3 gears will be plenty for me. I expect to be a casual
rider, not going for speed, and mostly wandering up to a coffee shop
or grocery store.

I have a six-speed bicycle, the first one I've had that wasn't a
coaster bike. I'm glad I got the six speeds, especially since we
have a few hilly roads around here. I don't ride fast, but there are
times when I even wish I had more.
(Come to think of it, it may be a 5-speed -- I forget!)

I have a (nominally) 24-speed bicycle, but that number comes from
multiplying the 3 gears on the chainring (at the pedals) times the 8
gears on the cassette (at the back wheel). In reality, there's a
tremendous amount of overlap in those combinations; and in practical
terms, I have a 10-speed . . . all eight rear gears connected to the
middle of the front gears (which is where I nearly always ride), then
from the lowest of those combinations, I can drop down one more step
on the chainring or, from the highest combination I can go up one step
on the chainring.

When I bought the bicycle (it's a road bike), I had them swap out the
standard chainring for a mountain-bike chainring for the lower gears.
The kind of riding I do, I don't need those high-end speeds, but I do
need all the help I can get on the steep hills.

On my previous bicycle, I used tires that were slick on the center and
knobby on the sides. In straight-ahead riding, I'd have the
low-resistance slick surface under me, and on corners I'd get some of
the knobby into play. Sounds great in theory, but the only time I ever
had the bike slide out from under me was on knobby tires--taking a
corner too fast. Equipment cannot replace common sense.

I do recommend Kevlar-lined tires. When I was commuting to work on the
bicycle, I got several flats from things as small as staples--just the
little, skinny things you use in offices. But after I put on the
Kevlar tires, I never had to change a tube again.

Oh, and my E-bike has just the sort of center slick, edge knobbed
tire described above. It weighs 80lbs, so I won't be leaning it much
anyway, but thanks for the warning. Next tires it gets will be
Bontrager Kevlars.